Change Master Page Dynamically
Here i the code that shows how to change master page of the page at runtime:
protected void Page_PreInit(object sender, EventArgs e)
if (Session["UserAccount"] == null) //check the user weather user is logged in or not
this.Page.MasterPageFile = "~/General.master";
this.Page.MasterPageFile = "~/Member.master";
Hope this will help !!!